FIG. 1A illustrates a block diagram of a general disk player and FIG. 1B illustrates a block diagram of a disk player having an anti-shock function added thereto.
A constitution of a general disk player is explained by referring to FIG. 1A as follows.
Referring to FIG. 1A, a conventional disk player includes an optical pickup device 100, a RF amplifier 105, an analog/digital converter (ADC) 107, a digital signal processing unit 110, and a control unit 125.
The optical pickup device 100 generates a light source to carry out a function of reading a record signal, and the RF amplifier 100 filters a RF analog signal which is read to input to carry out a shaping function.
The analog/digital converter (ADC) 107 samples the inputted RF signal with a constant speed according to a sample clock outputted from a sample clock generating unit to output to the digital signal processing unit 110.
And, the digital signal processing unit 110 carries out a signal processing on the digital data into a signal form recognizable by the control unit, and outputs the signal-processed data to the control unit 125.
FIG. 1B illustrates a block diagram of a disk player having an anti-shock function added thereto.
Referring to FIG. 1B, a disk player having an anti-shock function according to a related art includes an optical pickup device 100, a RF amplifier 105, an analog/digital converter (ADC) 107, a digital signal processing unit 110, a control unit 125, and a buffer memory 130.
The basic constitution of the disk player has bee explained in detail in FIG. 1A, which is skipped in the following description.
The disk player is very vulnerable to a shock due to its characteristics. When an external shock is impacted on the disk player, data of a disk cannot be read, whereby sound interruption is brought about in case of an audio disk.
Specifically, the external shock brings about severe problems in a portable disk player.
Hence, a disk player equipped with the anti-shock function is demanded.
A basic principle of a disk player equipped with the anti-shock function is explained as follows.
Data previously read from a disk are stored in a memory. When the data cannot be read due to the shock impacted thereon, the data having been stored in the memory are outputted, which is the basic concept.
While the stored data are outputted, the disk player reads the data again to prevent the problem of sound output.
Previously, a shock sensing is achieved by monitoring phase information of a servo system. When the shock is impacted on the disk player, a focus becomes abnormal to release PLL (phase lock loop). Thus, whether a shock occurs or not is sensed by monitoring the focus or PLL.
However, when the shock is sensed by monitoring the servo system, it is easy to sense a big shock. Yet, it is difficult to small shocks impacted continuously. For instance, when a portable disk player is used on jogging, walking, or driving a car, shocks that are not so big are continuously impacted thereon. When such small shocks are impacted continuously, it is unable to sense the shocks through the servo system.
In the related art, when a shock is sensed, an anti-shock function of a disk player is explained in detail as follows.
A buffer memory is provided for attaining a continuous data output when a mechanical shock that temporarily misaligns a read head with a data track on a disk occurs.
It is able to remove the influence that a shock having a limited time duration affects an output by means of reading data from the buffer memory. Namely, as far as a listener of the disk player is concerned, the shock has no influence on the output.
In order to achieve such a result, the data are read from the disk by high speed faster, i.e. twice faster, than that of reading the data from the buffer memory to record in the memory. In this case, as disclosed in EP-A-O 429 139, data are continuously read from a disk by high speed, a reading process is held when a buffer memory is full, and the reading process is resumed when the a prescribed portion of the buffer memory becomes empty.
Moreover, data are read from a disk by the same speed of reading data from a buffer memory for a normal time, the buffer memory is initially filled with the data before an output is initiated, and a reading speed of the data can be increased until the buffer memory is recharged when the buffer becomes empty by interruption of the data reading from the disk due to the head misalignment caused by a mechanical shock.
However, such an anti-shock function puts limitation on preventing the shock according to a capacity of the buffer memory. Namely, if the shock occurs for a period exceeding the capacity of the buffer memory, it is unable to prevent the shock anymore.
Namely, the duration time of the shock enabling to be compensated by the device is restricted by the capacity of the buffer memory. The shock of a compensation-available maximum length coincides with the time taken for reading the entire data inside the buffer memory.
Besides, if there is no sufficient time to recharge the buffer memory between a plurality of shocks, a series of shocks having the shorter duration time may exceed the memory capacity. Namely, as the frequency and number of times of the shocks increase, the buffer memory becomes emptied gradually.
For instance, if the device is applied to a portable disk player carried by a user participating in physical activities such as jogging and the like, continuous shocks may occur. Another example of generating the continuous shocks is that the device is used inside a car or other vehicles.
Thus, it is difficult for the related art to sense the continuous shocks as well as grasp the exact time point of the shock generation. Hence, it is difficult to judge whether to read the data again by deleting a certain amount of the buffer memory.